Jenkins and Lockette - who have combined for two catches in three NFL seasons - aren't the only young wideouts employed by the 49ers. But they are perhaps the best positioned to help lessen the sting of Crabtree's absence.

Jenkins, a first-round pick in 2012, and Lockette, who has the physique to match his eye-popping speed, spent much of the offseason connecting with a quarterback they didn't catch a pass from in 2012: Colin Kaepernick.

Jenkins, 23, and Lockette, 27, trained with Kaepernick in Atlanta for about two months during the offseason. The three lived together in Georgia and often spoke the same language: X's and O's.

Both receivers have struggled to master an NFL playbook, but Kaepernick's education has been more seamless. Last season, before his eighth NFL start, Harbaugh said Kaepernick's ability to absorb the divisional-playoff game plan was "savant-like." Jenkins and Lockette also give their 25-year-old tutor high marks.

"The way he explains things and the way he breaks it down, and one-on-one training with him, it's made me a different receiver, night and day," Lockette said. "Just learning the playbook from someone you can totally relate to. He understands how you think."

Said Jenkins: "Basically, learning the playbook kind of gave me the confidence to know what I'm doing. Just working with Kaepernick - getting on the same page as him."

Jenkins, of course, was invisible as a rookie. He had zero catches, played 47 snaps and dropped the only pass thrown his way.

Jenkins' lack of strength has been a topic of conversation since the day he was drafted. He had 12 reps of 225 pounds on the bench press at the 2012 NFL combine, a total topped by 29 of the 38 other receivers who lifted in Indianapolis. Hours after famously placing Jenkins' name in a draft-day envelope last year, even general manager Trent Baalke noted he needed to beef up his 192-pound frame.

A year later, Jenkins has added four pounds since February and hopes to play at around 200 pounds. Last week, he met the media outside the locker room in a sleeveless gray undershirt. Asked, jokingly, if his attire was meant to offer evidence of his offseason hours in the weight room, Jenkins smiled.

"I might try a little trend," he said. "I might have the guns out a little bit this year."

Jenkins, however, didn't mention his weight-room work when asked why he's entering his second season with confidence. Instead, he, again, referenced his enhanced knowledge of the playbook.

"Just looking at the rookies now, seeing what they're going through, I see myself in their shoes," Jenkins said. "I'm kind of the helping hand for them - they're kind of running around, and they're throwing plays at you left and right. You don't know which way to go. I was kind of in those shoes last year. So I kind of see how much as a player I've grown by seeing those guys."

For his part, the 6-foot-2 Lockette, who is a well-chiseled 211 pounds, is an NFL wideout from central casting. He won the Division II national title in the 200 meters at Fort Valley (Ga.) State and posted the second-fastest 40-yard dash time (4.37 seconds) at the 2011 NFL combine.

Still, his physical gifts have yet to translate on the field. He was undrafted after a 23-catch senior season, was released by the Seahawks last year and spent the rest of 2012 on San Francisco's practice squad after he was signed in late September.

Shortly after he joined the 49ers, he moved in with Kaepernick. And over the past eight months, Kaepernick has repeatedly quizzed him on assignments, sometimes during breaks in Warriors' games.

"During halftime, we go over plays - it's like, 'Hey, what do you have on this, this and that?' And I tell him my route and my conversion, if the defensive back does this or that," Lockette said. "Or, if I'm in the shower and he's walking down the hall, he'll say, 'Hey, Lock, what do you have on so and so.' I'll say, 'I have a go (route).' It's 24-7 learning. We make it fun for each other."

Now, Lockette and Jenkins hope the good vibes with their quarterback extend to the field. Given Crabtree's production in 2012 - 85 catches, 1,105 yards and nine touchdowns - it's possible both will be needed to help fill the void.

"The job we're competing for happens to be one of the most important jobs on this team - and that's replacing the best receiver we had," Lockette said. "We're not taking this lightly. Hopefully, we can replace Crab and hold it down until he gets back."